NiceHash provides a platform for users to mine for other cryptocurrencies and get paid in bitcoin. That could involve significant sums: it paid out millions of dollars in bitcoin every week, according to its official Facebook page.

The site said it was still working to figure out exactly how many bitcoins were taken.

The digital currency’s value has soared in recent weeks, crossing $15,000 for the first time on Thursday morning.

CoinDesk, a site specializing in cryptocurrency news and data, reported that NiceHash users were circulating a link to a bitcoin account that suggested as many as 4,736 bitcoins had been stolen, an amount worth roughly $71 million at current prices.

It wasn’t immediately clear whether funds had been taken from NiceHash users’ accounts as well.